Design of optical scanning system to detect volume and interferences in blood specimen in test tubes

In order to increase automatization and efficiency for a national reference laboratory, the ability to detect liquid and interferences in blood samples was investigated. Utilizing pairs of wavelengths of light, liquid and interferences can be detected regardless of the number of labels present on each tube. The absorption wavelength was selected at a wavelength where the measured intensity of the light significantly decreased when it passed through the condition of interest. The reference wavelength was selected so that when it passed through the sample, its intensity varied mostly from the number of labels placed on the tube and little from the presence of the condition of interest. These two intensities were measured and their ratio was computed in order to compensate for the tube material, number of labels, and ink on the labels. A liquid detection prototype was built and tested using this method. Tubes varying from no labels to six labels were investigated. The system was capable of detecting the presence of liquid at 0.4 mL and 4.6 mL with a tolerance of ±0.1 mL and ±0.2mL. For tubes with three labels on the all sides of the circumference, the accuracy of the system was 99.3%. For tubes with less than three layers on all the sides, the accuracy was 99.9997%.